My bad

That's something commonly said around here by way of acknowledging your mistake. It's not exactly an apology, just sort of saying 'I blew it'.

My turn
I thought I was supposed to have high expectations for my students, but you refused to even try. My bad.
I think you should be able to hear what's going on in class, not just what I say, but your classmates' responses as well, but it made you angry when I asked you to listen without interrupting. My bad.
I thought you wanted to be able to see the interactive whiteboard, so I changed your seat and then you stormed out. My bad.
I thought I was supposed to help my kids behave properly, but your feelings were hurt when I corrected your behavior. My bad.
I thought I was supposed to keep parents informed, but you were offended when I let you know what's going on. My bad.
I thought the counselor was here to help us, but you think I 'got' you in trouble by bringing in the counselor. My bad.
I thought you wanted advance notice when I set up a parent meeting, so I did that, but you still didn't show up. My bad.
I think my students need to learn basic calculation rather than algebra. At least then they'll be able to manage their finances. My bad.
I thought I was supposed to send the disruptive students to the team leader's classroom, but instead he made a ruckus in the hallway. My bad.
I think my students need to learn to read a newspaper and job aevertisements. My bad.
I thought the students were supposed to follow rules and procedures without outside intervention, but apparently you only take instructions from the school secretary. My bad. Guess we should have her teach class next week.